Hide unsupported pool APY estimates

[qingfeng312]

Summary

• Remove unsupported hardcoded monthly fee estimates from pool Fee APY.
• Display Fee APY and Total APY as N/A until reliable pool performance data is available.
• Update the APY footnote so the table explains why those values are hidden.

Verification

• npm ci
• npm run build

Bounty

Fixes #6

[qingfeng312]

Note on checks: the Vercel status points to an account deployment block. Local verification completed successfully with npm ci and npm run build.